Slippery when wet?
Isn’t salting road pavement supposed to keep it from getting slippery when snow arrives? Yes, but laying down liquid salt brine, which is what road departments in cold-climate states now use, will itself cause some slipperiness for trucks. And a while ago, that got the attention of several drivers for Clark Freight Lines out of Houston.
More specifically, what they saw was trucks spun off the road, presumably after running over pavement that had been treated with a liquid. That’s according to Danny Schnautz, president of the 170-truck, 600-trailer fleet and himself a former driver. He is also a member of OOIDA’s Board of Directors, and a discussion of this situation during a meeting is what led to this story.
“They told me this might be far worse than not having anything put down,” he said, describing a few past conversations with drivers who encountered freshly applied brine. “They saw how many trucks had spun off the road. One driver saw three guys along the side, in the median, that sort of thing, within 10 miles.”
Thankfully, they weren’t Clark rigs.
But those southern-based drivers were onto something that’s largely taken for granted by people in the North. Highway departments acknowledge that salt brine will initially make pavement slightly slippery, but not for long, because the watery part of the brine soon evaporates. The salt remains and clings to the pavement, because the brine has made it sticky. Beet juice is one substance commonly used in salt mixes. When snow falls onto the pavement, it melts when it hits the salt.
The Department of Transportation in Wisconsin, one of those cold-weather states, has published a bulletin describing the whys and hows of applying salt mixes to road surfaces. Part of it explains how their wetness can reduce traction:
“Slippery pavements may develop with anti-icing due to refreezing or to ‘chemical’ slipperiness. Refreezing can occur if the chemical is diluted, temperatures drop or blowing snow is trapped. Warm temperatures and high humidity can dilute chemicals with calcium or magnesium because of their high attraction for moisture. Pavements wet with deicing chemicals have slightly less friction than pavements wet with water.
“Some chemicals also go through a ‘slurry’ stage when they either dry out and return to a solid state or then hydrate and go from solid to liquid state,” the bulletin continues. “This ‘slurry’ stage is very temporary but causes an additional drop in friction (15%) on the pavement. This so-called ‘chemical’ slipperiness is not usually enough by itself to cause loss-of-control problems for highway traffic.
“However, when pavement temperatures are warm (45 to 50 degrees Fahrenheit) and dirt and oil come to the surface of the pavement, slippery conditions may develop for a short time, leading to claims of chemical slipperiness. Very few cases of slipperiness have been reported where salt brine was used.”
In Ohio, another state where wintry conditions require salt treatment, DOT spokesman Matt Brunning commented, “I’ve never seen a situation where brine treatment was so wet that it caused a vehicle to slip. And the brine has salt, so it’s not going to freeze.”
Many years ago, road department trucks spread rock salt – common sodium chloride – but it bounced as it hit pavement, and some of it landed alongside the roadway. There it leeched into the soil and killed vegetation. However, brine stays on the pavement, keeping salt where it’s needed and reducing the amount of material required for a given stretch of road. That saves taxpayer money, maintenance people say.
So, if you see that the roadway ahead has been freshly treated with salt brine, usually leaving telltale streaks on the pavement, expect some slipperiness simply because it’s initially a liquid – something like the moisture left by a light rain shower – and drive accordingly. LL